1. Field of the Invention (Technical Field)
The present invention relates to a test stand for unmanned air vehicles (UAVs) and/or micro air vehicles (MAVs) and more particularly to a multi-degree-of-freedom (DOF) gravity balanced UAV and/or MAV test stand.
2. Description of Related Art
It is a tremendous challenge to test autonomous flight capability of an UAV or MAV such as an autonomous helicopter. This is because the flying vehicle can crash or fly out of control when the flight control system does not perform properly. Such a situation can easily happen during an early test phase of the vehicle. To deal with this problem, a ground-fixed test stand is usually used to constrain the tested vehicle, so that it will not crash even if something goes wrong during a test.
However, a ground-fixed test stand has the drawback of adding extra load to the test vehicle, which is inconsistent with a real flight case. For small-scale UAVs, such as MAVs, this extra load may be too large to cope with. Therefore, active or powered test stands are sometimes used. Undoubtedly, active test stands are complicated in both design and operation. They are also subject to reliability problems. To continuously take advantage of the reliability and easy operation of passive test stands and also remove the burden of extra loading due to the weight of the moving part of the test stand, embodiments of the present invention comprise an innovative gravity-force balanced test stand.
Gravity balancing of a mechanical system or mechanism refers to the condition where no joint forces are required to keep the system or mechanism in equilibrium for all the configurations in its workspace. Basically, two approaches, namely, using counterweight or using springs, are available to achieve passive gravity balancing. However, using counterweight adds additional weight to the system resulting in larger moments and products of inertia of the system. Alternatively, gravity balancing with springs requires that the total potential energy (including both the gravitational energy and the elastic energy) of the mechanism remains constant. This approach keeps the mechanism balanced with a much smaller total mass. Some gravity balanced mechanisms using springs have been designed to serve as rehabilitation devices that compensate the gravity of patients' arms or legs.
Embodiments of the present invention comprise a multi-DOF passive UAV test stand that preferably employs springs to achieve gravity balancing at each configuration within the workspace. All of the weight of the entire moving part of the test stand is self balanced, such that no static load is exerted on the tested vehicle, allowing the UAV to be tested under a condition that is very similar to the free flight case.